Field of Invention
The invention relates to a method of evaluating a wear state of an assembly of a flow machine, in particular of a bearing arrangement of a pump or turbine, to an assembly of a flow machine as well as to a flow machine, in particular a pump or turbine.
Background Information
Bearings are used everywhere forces acting in specific directions have to be compensated or movements of an object in unwanted directions have to be prevented. In flow machines such as pumps or turbines, two kinds of bearings are essentially used in assemblies having rotating components, namely so-called radial bearings and axial bearings.
The bearings usually used in flow machines are in this respect very frequently assemblies of an extremely complex design in dependence on the specific application whose subcomponents are exposed to different, more or less strong wear mechanisms in operation. This applies both to radial bearings and to axial bearings.
In particular, but not only, mechanical seals and their individual parts are thus wear parts which will fail sooner or later. To delay this for as long as possible and thus to realize service lives which are as long as possible, before a servicing or a replacement of the bearings or their components, such as seals, becomes necessary, a whole number of very different measures are known in the prior art which are familiar to the skilled person per se.
In addition to the radial bearings for taking up radial forces, which in the simplest case can simply comprise a bearing saddle and a shaft which can rotate therein, with the shaft frequently, but not necessarily, being able to be sealed with a shaft seal, for example toward an external atmosphere, so-called axial tilting segment axial bearings are frequently also used for taking up axial forces whose design has long been well-known from the prior art. The general design principle in this respect provides that a plurality of bearing segments in the form of a ring-shaped grouping on a usually metallic carrier body are arranged about a bearing axis in a tilting segment axial bearing and are flooded with a circulating fluid as a lubricant in the operating state. The bearing segments per se comprise a metal, plastic, etc. in dependence on the use and often have the shape of a trapezoidal parallelepiped on whose side facing the carrier body a tilting element is located on which the bearing segment is supported. On the side of the bearing segments remote from the carrier body, a thrust collar is located by which the axial forces of the shaft are transmitted to the bearing, whereby corresponding pressure loads act on the bearing segments. This design principle will be explained even more exactly below with reference to FIG. 3a and FIG. 3b. 
When the thrust collar starts to rotate, a shearing of the fluid takes place between the thrust collar and the bearing segments and the thrust collar slides over the bearing segments. The forming of a wedge-shaped hydrodynamic lubricant film, which is an essential component in the operation of the axial bearing arrangement, results in a tilting of each bearing segment since they are supported on a tilting element. The start phase and the stop phase are particularly critical operating ranges for the tilting segment axial bearings, for example in pumps, since very high axial forces act in part in this respect. In these phases, the hydrodynamic lubricant film has not yet fully formed so that the thrust collar and the bearing segment contact one another directly without substantial hydrodynamic lubrication and wear occurs.
The bearing segments are generally mounted loosely and discretely with respect to the carrier body to avoid misalignments and to match the tilting of the bearing segments, which is effected by the formation of the hydrodynamic lubricant film, to the rotating shaft. The loose mounting is in this respect restricted in principle in that the bearing segments have to be held within the arrangement when the shaft does not rotate, that is for example in that the bearing segments are connected to one another by a flexible net or are fastened in a groove at the carrier body by means of a fastening means.
In dependence on the site environment, fluids having a low viscosity are in this respect used in part, for example a water-based lubricant or an oil mixture. In this case, the wear of the bearing segments is not a constant process, but damage to or destruction of the bearing segments often occurs within seconds at high pressure loads.
In this respect, such bearings, just like the radial bearings, are naturally also additionally always exposed to constant wear which finally has the result, even without sudden catastrophic effects, that the bearing or parts thereof have to be repaired or replaced.
In summary, it can thus be stated that in particular the rotating components or those components which are in contact with rotating parts are wear parts which will fail sooner or later. So that such a failure does not occur as a complete surprise, and thus possibly still worse damage is caused to further components of the corresponding machine, it is important already to obtain information on the wear state of a corresponding assembly before the final failure of such a wear part so that the wear state can already be reliably evaluated long before the final failure and preventive measures can possibly be taken.
Only very insufficient measures have previously been known from the prior art to monitor and evaluate the wear state of assemblies of flow machines, for example of bearings or bearing seals or bearing shafts of pumps or turbines or also of tilting segment axial bearings in the operating state.
It is thus known, for example with seals of radial bearings, to observe a leakage flow at the seal which can provide a certain insight into the wear state of the seal or of the corresponding bearing. It is, however, frequently also not possible at all to monitor the leakage flow during the operation of the machine or the information which is obtained by observing the leakage flow is too vague and indefinite to obtain reliable information on the wear state of the corresponding components.
It is in principle also known with both radial bearings and axial bearings, for example, to monitor the temperature of involved construction element components or of bearing fluids such as the temperature of oil which comes into contact with the parts to be monitored for wear in the operating state. This can take place more or less reliably, for example, using thermal elements or using electrical resistance thermometers and in principle allows a good monitoring and evaluation of a wear state of the assembly of interest. However, these methods are as a rule only suitable for laboratory purposes and test purposes since the temperature sensors have to be positioned in a complicated manner, frequently at very inaccessible sites. The measured signals generated by such temperature sensors furthermore have to be connected to corresponding measurement and evaluation instruments via electrical lines so that the use of the aforesaid temperature sensor is in most cases impossible under normal operating conditions across the board as is directly clear to the skilled person.